______ is the failure of chromosomes or chromatids to separate normally during meiosis

numbers

Accidents during meiosis

--Fertilization after nondisjunction yields zygotes with altered _____ of chromosomes.

Y

X

Sex chromosome abnormalities tend to be less severe, perhaps because of 

--the small size of the ____ chromosome or 

-- _____ -chromosome inactivation. 

The table below lists the most common human sex chromosome abnormalities. In general,  a single Y chromosome is enough to produce “maleness,” even in combination with several X chromosomes, and  the absence of a Y chromosome yields “femaleness.”

errors

polyploid

plant

New species can arise from ____ in cell division

Errors in mitosis or meiosis may produce _____ species, with more than two chromosome sets. 

The formation of polyploid species is 

--widely observed in many _____ species but 

-- less frequently found in animals

breakage

genetic disorders

cancer

Alterations of chromosome structure

Chromosome -_____ can lead to rearrangements that can produce 

-- _____ -___ or, 

-- if changes occur in somatic cells, ____ .

deletion

inversion

translocation

These rearrangements may include: 

a ______ , the loss of a chromosome segment,

 a duplication, the repeat of a chromosome segment, 

an ______ , the reversal of a chromosome segment, or  a -_____ , the attachment of a segment to a nonhomologous chromosome that can be reciprocal.

ri-du-chat Syndrome (Cat’s Cry Syndrome)

deletion

_____________● Infant’s cry is high-pitched, like that of a cat, due to incomplete development of larynx.

____ ____ -__ ● Individuals exhibit a range of developmental problems including delayed speech and language development, some degree of intellectual disability, and various features from the autism spectrum.

● Mutations in the Fragile X Mental Retardation-1 (FMR1) gene on the X chromosome result from an excessive number of “CGG” repeats (duplication).

▬ FMR1 gene produces a protein involved in normal brain development.

Chronic myelogenous leukemia (CML) 

22

9

______ ____ ____ is one of the most common leukemias, 

affects cells that give rise to white blood cells (leukocytes), and 

results from part of chromosome ____ switching places with a small fragment from a tip of chromosome ___

Two of the embryos will be trisomic for chromosome 18, and two will contain a single copy of chromosome 18.

In theory, when a nondisjunction for chromosome 18 occurs during meiosis I, four gametes can be produced. If these gametes are fertilized with unaffected gametes from the second parent, what observations would you make concerning the resulting embryos?

one

two

18

no

monosomy

A nondisjunction that occurs in the first meiotic division will result in ____ daughter cell having ____ copies of chromosome 18. This will be trisomic upon fertilization. The other daughter cell will have ____ copies of chromosome 18 and will contain a single copy of chromosome 18 upon fertilization, a condition known as ______ .

two

In a cell with eight chromosomes, one chiasma develops during meiosis I in only one particular pair of homologs. How many recombinant chromosomes will there be at the completion of meiosis II?

four

chiasma

This is because only two of the ____ chromatids present in a tetrad cross over at the ____ . The other two chromatids do not exchange parts and are unaltered. Also, only one set of homologous chromosomes went through this process.

somatic or body cells ... germ cells in the testes or ovaries

Mitosis occurs in _____; meiosis occurs in _____.

metaphase of mitosis

Looking through a light microscope at a cell undergoing division, you see that the condensed chromosomes have lined up along the midline of the cell. The homologous pairs are NOT joined in tetrads. Each chromosome takes its own place in line, independent of its homolog. You are witnessing _____.

haploid gametes ... diploid zygote

Fertilization joins _____ to produce a _____.

occurs in both mitosis and meiosis

Duplication of the chromosomes to produce sister chromatids _____

meiosis

If it weren't for _____, chromosome number would double with every generation of sexual reproduction.

16

Baker's yeast is an organism with 32 chromosomes that can perform asexual or sexual reproduction and exist as both a diploid and haploid cell. After meiosis, how many chromosomes will be present in each cell?

half

16

diploid

four

During sexual reproduction, meiosis reduces chromosome number by one-_____ , or to ____ in the case of yeast. This is because each chromosome is paired in a _____ cell and meiosis produces _____ haploid cells.

this brings the chromosomes into alignment so that crossing over can create new combinations of genes present on a single chromosome.

During meiosis I, homologous chromosomes form a tetrad. What does this accomplish?

Crossing over

____ ____ does this by exchange of corresponding parts between homologous chromosomes, creating a patchwork of maternal and paternal chromosome segments along a single chromosome.

homologous pairs.

arrangement

differ

In many organisms, including humans, chromosomes are found in _____ _____ Homologous chromosomes are identical in the ______ of their genes, but some versions of the genes may ___ between the chromosomes

locus

The order of genes at each _____ (position) along the chromosomes is the same, but there is the possibility for different forms of particular genes; for example, one chromosome may have the gene for freckles, the other may not.

Meiosis

Haploid

mitosis

Sexual life cycle of Diploid organisms involves _____ to form _____ gametes which join in fertilization forming a diploid zygote which develops into, by _____ , diploid organisms. Diploid organisms have homologous pairs of chromosomes including maternal chromosomes and paternal chromosomes.

independent assortment

crossing over

4

Meiosis includes Meiosis I in which ____ _____ occurs and ____ ____ occurs that results in genetic variation

During _____ chromosomes align single file along the equator of a haploid cell.

Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid.

telophase II

During anaphase I homologous chromosomes, consisting of sister chromatids, migrate to opposite poles.

At the end of _____ and cytokinesis there are four haploid cells.

At the end of telophase II and cytokinesis there are four haploid cells.

prophase II

centrosome

condensed

During _____ a spindle forms in a haploid cell.

Prophase II is essentially the same as mitotic prophase except that the cells are haploid

During interphase the _____ duplicates and the chromosomes are not _____ .

trisomy

You suspect that a serious developmental disorder is due to a chromosome abnormality and prepare a karyotype from an affected individual. In analyzing the karyotype, how could you distinguish trisomy from a chromosome structural defect such as a duplication?

-- In _____ there would be one extra chromosome; in a duplication, one chromosome would have two copies of a portion of the chromosome.

During meiosis, segments of nonsister chromatids can trade places. This recombination of maternal and paternal genetic material is a key feature of meiosis. During what phase of meiosis does recombination occur?

- Human- imposed selection has produced a variety of cats, dogs, pigeons and others

- Some breeds developed for specific purposes

- Dachshunds for badger pursuit

Heredity

Gregor Mendel

_____ is the transmission of traits from one generation to the next.

Genetics is the scientific study of heredity

____ -___

- Began the field of genetics in the 1860s

- deduced the principles of genetics by breeding garden peas

genes

character

trait

In 1866, Mendel described "heritable factors"

-- today called ____

A heritable feature that varies among individuals is called a ____ _,

- e.g flower color

Each variant for a character is a ____

- e.g purple or white flowers

true- breeding

___-_____ varieties result when self-fertilization produces offspring all identical to the parent

hybrids

cross-fertilization

The offspring of two different varieties are _____

The ______-____ of hybridization of genetic cross

stamens

Transfer

planted

Cross- Fertilization of Pea Plants

P generation

1. Removal of _____

2. ____ of pollen

3. Carpel matures into pea pod

4. Seeds from pod ____

-- Offspring (F1)

PP

aa

Bb

Connection between the previous explanation and chromosomes

Homologous chromosomes -- Gene Loci-- Dominant allele or recessive

Genotype: ___ - homozygous for the dominant allele

___ ; Homozygous for the recessive allele

____ , Heterozygous with one dominant and one recessive allele.

dihybrid cross

Mendel’s law of independent assortment

A_____ ______ is a mating of parental varieties that

differ in two characters.

Mendel performed the following dihybrid cross with the following results:

P Generation RRYY

Gametes RY

F1 generation -- RrYy

Testcross

______ - the mating between an individual of unknown

genotype and a homozygous recessive individual.

• Can show whether the unknown genotype includes a

recessive allele.

• Can be used to verify true-breeding genotypes

homozygous recessive

homozygous dominant

heterozygous

In simple dominant-recessive inheritance:

A = dominant allele

a = recessive allele

● The recessive phenotype always results from the

_____ _____ genotype (aa);

● The dominant phenotype can result from either

▬ the ______ _____ genotype (AA) or

▬ a ______ genotype (Aa)

malignant

A benign and a malignant tumor differ in that cells of a benign tumor remain within the tumor, whereas cells of a _____ tumor can spread to other body tissues

divide by mitosis

mitosis

When forming buds, hydras _____.

A hydra is a tiny multicellular animal that reproduces by sexual or asexual means. The bud cells in the hydra divide by _____ , and eventually the offspring will detach from the parent. The offspring will be genetically identical to the parent.

Mitosis

shorter

_____ does indeed take place during M phase, but M phase is _____ than interphase; cells spend most of their time in interphase

24

A certain species of animal has six pairs of chromosomes. How many DNA molecules are present in the nuclei of these animals during G2 phase?

S

24

DNA replication is completed during ____ phase, which occurs prior to G2 phase. Since each chromosome (12) is replicated, there are _____ DNA molecules in the nucleus during G2 phase.

A check that chromosome replication has been successfully completed

Chromosome replication

DO

A check that growth factors are present

A check that the cell is large enough for division

A check that nutrients are sufficient

Which of the following checkpoints does not occur late in G1?

____ ____ does not occur until after G1; this checkpoint is a G2 checkpoint.

variation

unique

Asexual and sexual reproduction differ in that sexual reproduction can produce great _____ among the offspring

As long as there is some genetic variation in the parents, different offspring will inherit ____ combinations of genes from each parent, creating variation among offspring

The chromosomes must be duplicated.

interphase

What must happen before a cell can begin mitosis?

Before mitosis can begin, the chromosomes, or genetic material, must be copied, which occurs during _____ .

Prophase

nuclear envelope

The centrosomes move away from each other and the nuclear envelope breaks up during which phase of mitosis?

Prophase is the first phase of mitosis, when the centrosomes begin moving toward opposite poles and the _____ _____ breaks up.

Metaphase

middle

The chromosomes line up in the center of the cell during which phase of mitosis?

Metaphase occurs in the middle of mitosis, when the chromosomes line up in the ____ of the cell.

Anaphase

opposite poles

The sister chromatids separate and begin moving toward opposite poles of the cell during which phase of mitosis?

•Must be homozygous recessive to exhibit the condition (rr) •Heterozygotes (Rr) do not exhibit the condition –Are called “carriers” of the condition

Dominant Inheritance

A pattern of inheritance in which the phenotypic effect of one allele is completely expressed within a homozygous and heterozygous genotype.

Incomplete dominance

Inheritance pattern where the phenotype of a heterozygote is intermediate between those of the two homozygotes; neither allele of the pair is dominant but combine and display a new trait

Antigen

-A molecule that binds to an antibody

foreign substance

simulates cells to produce antibodies

agglutination reaction

clumping that occurs when antigen, antibody bind

Law of Segregation

separation of alleles from each other during meiosis so that the gametes contain one from each pair

Law of independent assortment

*Alleles sort independently during Meiosis*Genes for one trait do not influence inheritance of genes for another trait.

parental phenotypes

offspring with same phenotype as parents

when the offspring of two parents look like the two parents

Recombinant Phenotypes

Offspring with phenotypes that recombine parental traits

crossover

an exchange of genetic material between homologous chromosomes.

sex chromosomes

determine the sex, females xx and males xy

sex linked/sex linked genes

genes located on the x chromosome

genes on y chromosome are also sex linked

X-linked recessive gene shows its effects more in men than women b/c men only have one x

sex linked/sex linked genes

genes located on the x chromosome

genes on y chromosome are also sex linked

X-linked recessive gene shows its effects more in men than women

females may show recessive trait when she has two recessive copies

wild-type

___--___ traits, those prevailing in nature, are not necessarily specified by dominant alleles.

- most common allele, genotype, or phenotype present in a population

two

recessive'

heterozygous

Inherited human disorders show either

 recessive inheritance in which

 ____ _______ alleles are needed to show disease,

 _____ parents are carriers of the disease-causing allele, and

increases

one

eliminated

the probability of inheritance _____ with inbreeding, mating between close relatives

dominant inheritance in which

 ____ dominant allele is needed to show disease and

 dominant lethal alleles are usually _____ from the population.

cystic fibrosis (CF),

recessive

1 in 31

The most common fatal genetic disease in the United States is ____ ___ resulting in excessive thick mucus secretions. The CF allele is

 ____ and

 carried by about ___ in ___ Americans.

Achondroplasia

Huntington’s disease,

Dominant human disorders include

 ______ , resulting in dwarfism

 ______ ____ a degenerative disorder of the nervous system.

complete dominance.

incomplete dominance

both

Mendel’s pea crosses - always looked like one of the parental varieties, called ____ ____

 For some characters, the appearance of F1 hybrids falls between the phenotypes of the two parental varieties. This is called _____ _____ , in which

 neither allele is dominant over the other and

 expression of ____ alleles occurs.

Genotype

three

_____ = two different alleles; sometimes, more than two alleles exists in the wider population.

 Human ABO blood group phenotypes involve ____ alleles for a single gene.

heterozygous

codominance

The four human blood groups, A, B, AB, and O, result from combinations of these three alleles.

 The A and B alleles are both expressed in _____ individuals, a condition known as _____ .

homozygous

imagine that long fins in zebrafish is a dominant trait. A breeder wants to set up a breeding program beginning with homozygous dominant long-finned fish. If she obtains a handful of the long-finned fish, how can she tell which if any of these are homozygous for the trait?

Cross the long-finned fish with short-finned fish; if the offspring are all long-finned, the long-finned parent is _____ .

testcross

This cross is a _____ (the short-finned fish must be homozygous recessive), and having all offspring show the dominant trait proves that the long-finned parent is homozygous.

Lethal dominant alleles are harmful whether they are carried in homozygous or heterozygous form, so there is always strong selection against these alleles.

recessive

Why are lethal dominant alleles so much more rare than lethal recessive alleles?

The ability of lethal _____ alleles to "hide" from selection in heterozygotes accounts for their prevalence relative to dominant alleles, which are always visible to selection.

EEGgcc

An insect that has the genotype EeGGcc will have the same phenotype as an insect with the genotype _____.

GG and Gg.

Individuals with one or two dominant alleles of a gene are indistinguishable, so EE and Ee have the same phenotype, as do___ and ___

50

50

Snapdragons show incomplete dominance in their flowers. A pink snapdragon is crossed with a red snapdragon. What color(s) are the offspring?

The cross of a homozygous dominant with a heterozygote will produce ____ % red flowers and ____ % pink flowers.

Genetics

chromosomes

autosomes

sex chromosomes

sex-linked

alleles

homozygous

heterozygous

dominant

recessive

___ -- studies of inheritance of genes-- which are located on ____ . Non-sex-related ones are called _____ . Sex-related ones are called ___ ____ which have genes that determine ____-____ traits. Genes come in alternate forms called ____ . When copes are the same (ff) it is called ____ . When copes differ (Ff) it is called _____ . Expressed allele is called _____ . Unexpressed allele is called ____

second filial generation

F2

grandchildren

In a test cross, F2 refers to he ____ _____ ____ , or the "grandchildren" of the original mating pair

____ is shorthand for second filial generation, or the "_____ " of the original mating pair.

Do a test cross between two true-breeding individuals and observe the trait expressed by the F1 plants.

hybrids

dominant

Imagine a particular trait that is determined by a single gene. If this gene is present in two forms, how can you tell which allele is dominant and which is recessive?

the F1 plants are _____ that contain both forms of the gene, so the trait the F1 plants display is the ____ trait.

They should be informed that if they have a child, the child will not have Tay-Sachs disease but will have a 50% chance of being a carrier of the Tay-Sachs allele.

Imagine you're counseling a couple who have undergone carrier screening for Tay-Sachs disease. The man is a carrier, and the woman does not carry the Tay-Sachs allele. How should you advise them?

because the woman will transmit a normal allele to the child, the child will not be affected; however, there is a 50% chance that the child will inherit a Tay-Sachs allele from the father and thus be a carrier.

character

trait

monohybrid

alleles

-a _____ is an inherited feature that varies from individual to individual

- A _____ is one particular variation of a character

- A genetic cross involving parents that differ in a single character is called a ______ cross

- Most human genes come in alternative versions called ____

dominant

recessive

phenotype

genotype

-If an organism has two non-identical versions of a gene, that one that is expressed in the organism is called the _____ allele

- If an organism has two-identical versions of a gene, the one that is not expressed in the organism is called the _____ allele

- The physical traits of an organism are called its _____

- The _____ is the genetic makeup of an organism

1/4 (25%) will by AB, type AB blood; 1/4 will be AO, or type A Blood;

1/4 will be BO, or type B blood;

1/4 will be OO, type O Blood

A man who has type Bblood marries a woman who has type Ablood. What blood types are possible for their children?

Pleiotropy

Sickle-cell

shape

anemia

codominant

malaria

_____ occurs when one gene influences many characteristics.

______ ____ disease is a human example of pleiotropy. This disease: affects the type of hemoglobin produced and the _____ of red blood cells and

causes _____ and organ damage.

Sickle-cell and nonsicklealleles are _______ .

Carriers of sickle-cell disease are resistant to _____ .

polygenic inheritance

•Human skin color

Many characteristics result from ____ ____ , in which a single phenotypic character results from the additive effects of two or more genes.

___________ is an example of polygenic inheritance

Weight

Height

Intelligence

behavior

Other examples of polygenic inheritancein humans:

•Hair color

•Eye color

•____

•____

•______

•Many forms of ____

heredity

environment

inherited

Many characters result from a combination of ____ and the _____ . For example,

skin color is affected by exposure to sunlight,

susceptibility to diseases, such as cancer, has hereditary and environmental components, and

identical twins show some differences.

Only genetic influences are ____ .

Genes

segregation

independent assortment

The chromosomal theory of inheritance:

____ occur at specific loci(positions) on chromosomes, and

Chromosomes undergo _____ and ____ ____ during meiosis.

law of segregation

law of independent assortment

The ____ ___ ____ depends on separation of homologous chromosomes in anaphase I.

The ______________ depends on alternative orientations of chromosomes in metaphase I.

linked genes

Bateson and Punnett studied different characters in sweet pea plants that did not show a 9:3:3:1 ratio in the F2 generation. This is an example of ____ ____ , which are located close together on the same chromosome tend to be inherited together.